Conventionally, for example, there has been known a technique of generating an overhead view image in which a vehicle is looked down from a virtual point of view based on images captured by a plurality of cameras mounted in the vehicle in order to contribute to vehicle driving assistance. For example, there is a technique of normalizing a plurality of images obtained from a plurality of fish-eye cameras capturing an area around a vehicle and generating an overhead view image in which all areas around the vehicle are looked down from a virtual point of view above the vehicle using the normalized images. Further, for example, there is a technique of generating an overhead view video whose point of view is converted to a video imaged from directly above an own vehicle based on videos imaged by a plurality of camera devices imaging a video around the own vehicle.
In the technique of generating the overhead view image, the overhead view image in which all areas around the vehicle are looked down is generated by projecting camera videos on a plane surface corresponding to a road surface. For this reason, for example, an image may be distorted at the position away from a vehicle as illustrated in FIG. 27. FIG. 27 is a diagram illustrating an example of an overhead view image in which all areas around a vehicle are looked down.
On the other hand, there has been known a technique in which an omnidirectional image whose virtual point of view can be arbitrarily changed is generated by synthesizing camera images acquired by a plurality of cameras installed around a vehicle. In the omnidirectional image, since a projection plane of a camera image is stereoscopic, distortion of an object present at the position away from the camera, that is, at the position away from the vehicle is smaller than in the overhead view image whose projection plane of a camera image is a plane surface. Thus, in the omnidirectional image, the position away from the vehicle can be more clearly checked than in the overhead view image, and so the omnidirectional image may be more useful to the vehicle driving assistance.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2006-253872
Patent Literature 2: Japanese Laid-open Patent Publication No. 2009-298178
Meanwhile, in the omnidirectional image, images of a plurality of cameras are synthesized. Thus, an object captured in an area within a common capturing range of a plurality of cameras, that is, an overlapping area is included in a plurality of camera images. For example, when cameras are installed at four positions, that is, the front, the rear, the left, and the right of the vehicle, there is a difference of several meters between installation positions of cameras. The difference between installation positions of cameras causes parallax between camera images, and thus the following problem occurs in the overlapping area of a plurality of cameras on the omnidirectional image. For example, when two camera images are synthesized on the overlapping area, one object is viewed as two objects since the object is projected at a plurality of positions on the projection plane. In addition, when, of two camera images, an image to be employed on the overlapping area is decided by a certain line on the omnidirectional image, an object present across the line, for example, road surface paint, is viewed in a broken state.